Epidemiology and Evolution of Invasive Pneumococcal Disease Caused by Multidrug Resistant Serotypes of 19A in the 8 Years After Implementation of Pneumococcal Conjugate Vaccine Immunization in Dallas, Texas

Department of Pediatrics, Division of Infectious Diseases, University of Texas Southwestern Medical Center, Dallas, TX, USA.
The Pediatric Infectious Disease Journal (Impact Factor: 3.14). 11/2009; 29(4):294-300. DOI: 10.1097/INF.0b013e3181c2a229
Source: PubMed

ABSTRACT The heptavalent pneumococcal conjugate vaccine (PCV7) has significantly reduced vaccine-type invasive pneumococcal disease (IPD) in children. An increasing percentage of IPD cases are now caused by nonvaccine serotypes. The purpose of our observational study was to define the epidemiology of pneumococcal disease in Dallas, TX children for 8 years after implementation of PCV7 immunization.
Streptococcus pneumoniae isolates from normally sterile sites were collected at Children's Medical Center of Dallas from January 1, 1999 to December 31, 2008. Incidence of IPD was calculated using inpatient and emergency center admissions to Children's Medical Center of Dallas as the denominator. Isolates were serotyped and penicillin and cefotaxime susceptibilities were determined. Serotype 19A isolates were further characterized by multilocus sequence typing.
Compared with the prevaccine period of 1999-2000, there was a significant reduction in the incidence of IPD from 2002 to 2008 (P < 0.05), although a significant increase in IPD incidence was observed from 2006 to 2008 (P = 0.038). The number of IPD cases caused by serotype 19A increased from 1999 to 2008 (P < 0.001). There were significant increases in penicillin and cefotaxime nonsusceptible 19A isolates during this 10-year period (P < 0.001 and P = 0.004, respectively). The most common sequence type (ST) of the 19A isolates was ST-199 (42.7%). Clonal complex (cc-156) and cc-320 emerged in the period of 2005-2008 as penicillin and cefotaxime resistant 19A strains.
In Dallas, PCV7 immunization reduced significantly the incidence of IPD caused by vaccine-type strains. A significant increase in IPD caused by serotype 19A was observed. The penicillin and cefotaxime nonsusceptible STs, not previously identified in Dallas, have recently become an important cause of IPD.

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    • "Pneumococcal serotypes are defined by the chemical structure of the capsular polysaccharides, and pneumococcal serogroups consist of structurally related serotypes that in some cases share some immunological cross-reactivity. However, crossfunctional responses, as defined by the opsonophagocytic activity (OPA) assay, and crossprotection provided by immune responses to related serotypes may vary between individual serotypes within serogroups While strong immunological cross-reactivity by ELISA has been demonstrated in some cases, e.g., serotypes 19A and 19F, little cross-functional activity in OPA assays and no evidence of cross-protection has been observed in human populations for these two related serotypes [9] [10] [11] [12]. "
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    • "All three clones have persisted into the post-vaccine population with a new serotype not targeted by the vaccine, and in each the predominant serotype is 19A. The most successful and clinically significant is ST 320 (Beall et al., 2006; Beall et al., 2011; Brueggemann et al., 2007; Pai et al., 2005b; Pelton et al., 2007; Techasaensiri et al., 2010), which is a close relative of ST 236, Taiwan 19F -14. In addition to an important role in invasive pneumococcal disease (IPD), ST 320 is increasingly common in carriage (unpublished observations). "
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    • "After some years of PCV7 use, the incidence of pneumococcal diseases caused by serotypes included in the vaccine has drastically reduced and, in addition, the transmission of these serotypes has also decreased (Dagan, 2009; Pilishvili et al., 2010). Nevertheless, a substitution of the prevalent disease-causing serotypes was observed, making necessary the adoption of new formulations such as PCV10 or PCV13, to adequate the vaccine to the new circulating strains (Bettinger et al., 2010; Hsu et al., 2010; Techasaensiri et al., 2010). Therefore, broad coverage of conjugated vaccines is attained by the inclusion of several polysaccharides in the formulation, a practice that increases the production costs. "
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